The term “deficit irrigation” is used to describe the situation where all available water from a given water source is used to irrigate a given parcel of land. Frequently, the source cannot supply sufficient water volume to irrigate the entire parcel simultaneously. Under these conditions, the parcel is typically subdivided into a plurality of zones, and the water flow is periodically directed to each zone, or to combinations of zones, such that over a given period of time each zone receives an equal share of the available water.
In deficit irrigation situations, it is not unusual to use a continuous-flow irrigation system wherein the water source operates continuously. The source may be a water well powered by a gas or electric pump. The water from the source is periodically switched between irrigation zones, but it never shuts off during normal operations. If the water distribution system operates incorrectly when the source is running, an emergency shutdown of the source may be required to protect the distribution lines from overpressure and failure.
In the typical continuous-flow irrigation system, electrically-operated valves control the flow of water from a source header to the delivery lines for each zone. A programmable timer is used to operate the zone valves in a predetermined sequence to distribute the water as desired. However, prior art irrigation timers typically require the user to independently program the watering schedule for each zone by specifying start times and watering duration for each valve (or group of valves). A persistent problem with such prior art timers is the significant amount of calculations and programming input (i.e., button pushing) required to program the timer so that it runs 24 hours per day (i.e., no gaps between end and start times in successive zones) and so that it evenly distributes the water to all zones over the day. A need therefor exists, for a continuous-flow irrigation timer that controls the distribution of water between zones with a minimum of user input.